Pivot portion of a piston shoe in radial pistol devices

ABSTRACT

In radial piston fluid handling devices, such as for example pumps or motors, piston shoes are pivotable connected to the respective pistons. The invention improves the swing-member portion of the piston shoe in order to increase the efficiency and pressure bearing capability thereby, that the endface of the pivot portion is formed part-cylindrically by a radius which is a little bit shorter than the radius of the associated piston. The fluid pressure balancing pocket in the pivot member becomes formed accordingly, so that the pressure bearing capacity of the piston-piston-shoe pivot-assembly becomes considerably improved.

BACKGROUND OF THE INVENTION

It is known for example from my U.S. Pat. No. 3,277,834 that a pistonshoe is inserted between the actuator of the piston stroke and therespective piston in radial piston type fluid handling devices. From thesaid patent it is also known, that the piston shoe is provided with apivot portion of part-cylindrical configuration in order to swing orpivot in a respective bed of the piston. Fluid pressure balancingpockets were associated to the pivot portion in order to reduce frictionbetween the piston and piston shoe.

Those piston shoes have operated satisfactorily in the past. However, innewer times the rotary velocities of such devices is increased and thepressure in fluid is also increased in radial piston type fluid handlingdevices. Thereby it appeared, that the total efficiency decreased, whenthe rotary velocity or pressure was increased. According to thisinvention it has now been discovered that to a large extent the loss ofefficiency came from a too narrow size of the bearing face of the pistonshoe's pivot member and by an unsuitable configuration of the ends ofthe pivot portion and of the location and size of the fluid pressurebalancing recess associated thereto. These drawbacks are overcomeaccording to this invention thereby, that the end face of thepart-cylindrical pivot portion of the piston shoe becomes formed as apart-cylindrical face with a radius of a slightly shorter size than theradius of the associated piston is. The fluid pressure balancing recessbecomes extended in size and its walls are configurated to conformsubstantially to the invented end face configuration, but leaving enoughspace to form a suitable sealing face. Further improvements consist inan inclination on the piston-most portion of the end-portions of thepivot member or in the increase of the radius of the bearing face of thepivot portion.

SUMMARY OF THE INVENTION

The main object of the invention is, to overcome the drawbacks of theknown pivote portion of the known piston shoe.

In order to achieve this main object of the invention, the first objectof the invention is, to increase the bearing portion-size of the pivotmember or portion of the piston shoe. The increased size of the bearingface results in the capability of bearing a higher pressure in fluid orin a reduced load per unit of face in case of small pressure in fluid inthe device.

The second object of the invention is, to reduce the friction betweenthe pivot portion and the bed of the piston. Thereby the efficiency ofthe device is increased.

The third object of the invention is, to increase the pressure in fluidin the device and to increase the working speed of the device. Therebythe power of the device for a given size and weight will be increased.

In order to reach and materialize the objects of the invention thefollowing provisions of this invention are done, either single or incombination:

The first provision of the invention is to provide an end-faceconfiguration to the pivot member of the piston shoe to becomepart-cylindrically shaped with a radius around a middle line of thepivot portion.

The second provision of the invention is, to make the radius of thefirst provision a little bit smaller, than the radius of the associatedpiston is.

The third provision of the invention is, to provide an inwardsinclination of small, but suitable size on the end face of the first orsecond provision. This inclination prevents touching or scratching ofthe end face of the pivote portion on the associated cylinder wall.

The fourth provision is, to extend the fluid pressure balancing recessin the pivot member to such extent, that only a relatively short sealface remains between the end of the pivot member and the fluid pressurebalancing recess. Thereby the mechanical friction on each other betweensliding faces becomes reduced. This provision further assures, that theremaining seal face (s) remains lubricated enough at all times. Theheretofore used too long seal face was not lubricated enough. It hasbeen found in accordance with this invention, that the seal face of thepivot portion of the known art was too long, which resulted teherein,that the endmost portion was not enough lubricated and began to wearoff. The wear-off material particles then entered the further portiongradually by time and disturbed the seal face entirely over arespectively long time of use. The shortening of the seal face by thisinvention prevents this failure of long life of the pivot portion of theformer art.

The fifth provision of the invention is, to give the endwalls of thebalancing recess of the fourth provision a radius around a middle lineof the pivot portion, whereby said radius is respectively suitablyshorter than the radius of the end face of the first and secondprovision.

The sixth provision is, to make the endwalls of the balancing recessinwardly inclined in order to give strength to the sealing portion onthe end of the pivot portion and also to increase the length of the sealface at locations little remote from the piston centre, because at theselocations the clearance between the seal faces increases, wherefore thelength of the seal faces is to be increased at these portions in orderto obtain an efficiency maximum as discovered and desired by thisinvention.

The seventh provision of the invention is, to maintain a verticalbearing face portion or portions on the pivot portion. Because it is animportant discovery of this invention, that ball-part-formed pivotmembers suffer a braking action thereby, that the wide balancing recessis bordered by seal faces, which are stiffly inclined, whereby the pivotportions of the piston shoes of former art became clamped in therespective piston portions, almost like a cone in a coned taper. Thebalancing recess of the former art in ball-part-formed pivot portionshas therefore contrary to the expectations of the former art, not servedto prevent friction, but resulted in increased friction or even brakingor clamping in the bed of the pistion. These mistakes of the former artare recognized and found by this invention. The provision of a bearing-or seal-face portion vertical to the bottom of the bed in the pistonshoe prevents any kind of clamping or braking in a cone-like face.

The eigth provision of the invention is, to provide a control corner inthe medial portion of the pivot portion for the purpose of controllingthe flow of fluid into balancing recesses in the associated pistons inorder to make it possible to locate the balancing recesses in thepistons more properly more outward, than it was possible in the formerart. Thereby the friction between the piston and the cylinder wall isreduced especially at large piston strokes and powers.

The nineth provision of the invention is, to extend the balancing recessendwards of the control corner more deeply into the pivot portion inorder to obtain a maximum of efficiency of the balancing recess and ofthe piston-piston-shoe pivot assembly.

The tenth provision of the invention consists in the provision of anassociated balancing recess in the bed of the piston, which isassociated to the respective pivot portion of the piston shoe.

The eleventh provision of the invention consists in the application ofthe extension of the pivot bed and face over almost the entirecross-sectionional extension of the piston by increasing the radiusaround the pivot portion axis to 0.8 to 1.3 of the radius of the piston.Thereby the bearing surface size is increased extensivley. At the sametime the medial tangent on the pivot assembly is reduced, so, that themedial bearing force direction becomes more close to the direction ofthe medial load. This provision reduces friction further, because itextends the size of the bearing face, it extends the size of thebalancing recess and it prevents further friction between stifflyinclined portions. And, the twelfth provision of the invention is, toassure a maintainance of contact between the faces of the pivote portionof the piston shoe and the bed of the piston by the application of anassembly or holding means, for example a pin and thereto associatedmembers for the prevention of escape of the piston shoe's pivot portionfrom the bed of the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view through a pivot assembly of the former art.

FIG. 2 is a sectional view through another pivote assembly of the formerart.

FIG. 3 is a cross-sectional view through FIG. 2 along the line III--III.

FIG. 4 is a sectional view through a piston-piston-shoe pivot assemblyof the invention.

FIG. 5 is a cross-sectional view through FIG. 4 along the line V--V.

FIG. 6 is a sectional view through FIG. 4 along the line VI--VI.

FIG. 7 is a view onto the bottom of the pivot portion of FIG. 4 seenfrom the line VII--VII.

FIG. 8 is a sectional view through another embodiment of apiston-piston-shoe pivot assembly of the invention; and:

FIG. 9 is a cross-sectional view through FIG. 8 along the line IX--IX.

FIG. 1 demonstrates a sectional view through a pivot piston-piston-shoeassembly of the former art, wherein the pivot portion of the piston shoeis partially a ball. Said part-ball is borne in a respectivelyhollow-ball-part shaped bed in the piston 42. Referential 41 shows thesaid part-ball formed portion of the pivot portion of the piston shoe. Afluid pressure balancing recess 43 is provided in the piston's bed.Fluid is led into it through passage 44. According to this invention ithas now been discovered, that this arrangement of the former art shouldhave the purpose of eliminating or reducing friction between the facesof the members, does actually not reduce the said friction, but on thecontrary it increases the friction. That can be understood therefrom,that a face contact consists only outwards of the balancing recess 43.The pivot portion 41 is pressed by fluid pressure towards the piston 42,whereby said force acts substantially in the direction of the axis ofthe piston. According to this invention, a tangent 51 is drawn onto themedial of the contating bearing faces portions. By simplyfying thepart-ball form to a cone between the tangents 51 it will be seen, that,as wider as the balancing recess 43 is, as stiffer becomes the tangent51 of said cone. In case of a very stiff tangent or medial tangent 51due to a large balancing recess 43, the cone comes into the self-brakingrange, so, as for example cones and tapers are used in machine tools forsticking a taper non-moveable into a cone. Thus, if the balancing recess43 is relatively wide, the piston shoe's pivot portion 41 becomesentirely stuck within the medial cone of the bed of piston 42. Pistonand piston shoe are then so strictly blocked within eachother, that thepiston shoe cannot pivot any more. If in the device the piston shoe ispivoted by force, the faces between piston and piston shoe weld ineachother and scratch or wear off in short time. When the fluid pressurebalancing recess 43 becomes made relatively small in size, the blockingaction as described above is prevented, but than the balancing recessdoes not provide effective reduction of load on the bearing faces. Itfails to serve its purpose. The above described matters and effects haveobviously not been sufficently discovered until now, because commonlyfluid handling devices are only tested as a whole assembly. Thereby thedescribed matters substantially escaped the attention. This discovery ofthe invention demonstrates most effectively, why the invention preventssuch terrible drawbacks of the former art.

The assembly of FIGS. 2 and 3 is substantially the assembly of my olderU.S. Pat. No. 3,277,834. The pivot portion 31 of the piston shoe isborne in and embraced partially by the bed of the piston 32. Pivotportion 31 is of part-cylindrical shape with an axis normal to the axisof the piston and the ends of said pivot portion are planes, which arenormal to the axis of the pivot portion 31. A small rectangular fluidpressure balancing recess 33 is provided in the pivot portion 31 and isfilled with fluid under pressure by passage 34 through piston 32. Due tothe fact, that the ends were planes, normal to the axis of pivot bar 31,the pivot portion 31 had to be short. Its length had to be substantiallyshorter than the diameter of the associated piston. Because otherwise,during pivoting motion the end corner of the pivot portion would touchand scratch on the wall of the respective cylinder wherein the pistonmoves during operation of the machine.

According to this invention it has now been discovered, that the saidassembly of FIGS. 2 and 3 of the former art had the following failures:

(a) The portions of the face of the piston bed located beyond the end ofthe relatively short pivot portion 31 wre not utilized for bearingpurposes, whereby the bearing capacity of the assembly remained limited.

(b) The rectangular balancing recess was boardered by much too longsealing surfaces. The result thereof was, that the endportions of thebearing faces were no more lubricated, because under the tight fit underload the fluid could enter only a short distance into the clearance,which became so narrow, that almost no clearance remained. The endportions of the bearing therefore run dry, which resulted in wear offand in moving of worne off material particles into th rest of thebearing, when pressure and/or relative velocities became too high.

The above described failures or drawbacks of the former art have beennarrowed or entirely overcome by the improvements which are done by thisinvention and which are demonstrated in the figures, which are discussedin the following.

In FIGS. 4 to 7 one embodiment of the invention is shown. FIG. 4 shows,that according to the invention the end of the pivot portion 1 isprovided by an endface 101 which is partial cylindrically around theaxis 30 and defined by radius 5. Radius 5 is a little bit shorter, thanradius 55 of piston 2. Thereby the bearing face of the pivot portion isextended to a maximum of bearing area and still the pivot portionsmaintains its ability to move within the bed of the piston 2 and withinthe respective cylinder of the device. In order to prevent scratching ofthe cylinder's wall by the bottom corner of the end face 101 of thepivot portion during wide pivoted position, the bottom portion of theends 30 are provided with a small inclination 6. The form of the ends101 of the pivot portion 1 can be clearly seen in FIG. 6 and this figureshows also the relation of the pivot portion relative to the piston 2.Radius 5 is clearly demonstrated and the holders 62 of the pistons 2 arealso shown, but they are no novelty of this invention. A further featureof the invention is the extension of the fluid pressure balancing recess3 over a wide area of the pivot portion 1, so, that the remaining sealface portions are short enough but maintain the needed length in ordernot to wear dry but still to seal effectively. The best form is, toprovide the end of the balancing recess 3 partially by a radius 8 aroundthe same centre 30 of pivot member 1. The difference 5 minus 8 definesthen the accurate seal face length. In order, that the sealing portionsremain stiff enough to withstand deformation under high fluid pressurein recess 3, the inwardly directed inclined walls 7 are provided in thepivot portion 1. This inclination 7 of the invention serves however notonly the purpose of strength but an additional purpose of the invention,namely to extend the length of the seal face portions as more, asfarther as they are located away from the bottom of the bed in thepiston 2. According to the invention, the bottom portion is so stronglypressed against the piston's bed, that the faces are so extremely closetogether, that the clearance there is almost zero. Consequentely inaccordance with the invention the length of the seal face must here bevery short. But, as seen in FIG. 5, the part-cylindrical configurationprovides, that in the height of the axis 76 of the pivot bar 1 the facesare normal to the face direction of the bottom. Consequenetely in thisarea is no pressing force, which would press the seal faces together.Therefore, at these locations the clearance between pivot bar 1 andpiston's bed appears. Leakage would escape through this clearance, ifthe seal faces would be short here. Therefore, the inclination 7 servesthe purpose of extending the length of the seal faces as more as fartheras the portion of the seal faces is remoter from the bottom of the bedin the piston 2. Thus, the inclination 7 provides an ideal condition forsealing and bearing of the pivot member 1 in the bed of the piston 2.

It is further seen from FIGS. 4 and 5, that a resepctive fluid pressurebalancing recess 53 in piston 2 may be associated to the recess 3 inpiston shoe bar 1. Thus, if the piston shoe 1 pivots extensively, it canbe seen in FIG. 5, that then the recess 3 dislocates from the centre ofthe axis of the piston 2. A portion of the bearing bed or of the pivoteportion 1 would then be insufficiently lubricated and balanced.Therefore at the respective portion, the lubrication and balancingaction of fluid pressure is taken over partially by the recess 53 in thepiston 2. At non-pivoted position the recess 53 has no purpose ofaction.

In FIG. 4 and 5 the control-corner 8 is provided. This corner has thepurpose of controlling the flow of fluid under pressure into thepassages 9 of FIG. 5 and therethrough into the piston's tangentialbalancing recesses 52. The balancing recesses 52 and the passages 9 inpiston 2 are no novelty of the invention. In the former art however, therecesses 52 were located too wide inwards of the pistons. Therefore theywere not very effective in operation. This was due to the too smallbalancing recess 53 of the former art. According to the invention thecontrol corner 8 is so far distanced from the bottom of the piston'sbearing bed, that the passages 9 can be provided more in the top portionof the piston 2. Thereby the passages 9 can be drilled normal to theaxis of the piston and thereby become set more accurately, while therecesses 52 can be located more towards the top of the pistons 2 andthereby become more effective in operation of the device. The controlcorners 8 are closing the passages 9 in central position of non-pivotedlocation and they open either one of the passages 9, when the pistonshoe pivots in the respective extent in the one or the other direction.

According to the invention it has also been discovered, that the formercontrol corners prevented the needed lubrication of the upper portionsof the seal faces of the piston's bed and pivot portion 1. Therefore,according to the invention the fluid pressure balancing port 3 of theinvention is endwards of the control corners 8 extended more inwardlyinto the pivot portion 1, beyond the control corners 8. This providesthe good lubrication of the seal faces area in the height of the axis76. According to this invention, a flow through restriction by a narrowpassage 90 may be provided in the piston 2 in order to prevent excessiveflow of fluid into the pivot bar and its surrounding. It is preferred todrill a bigger bore from the bottom into the piston 2 and insertthereinto a filler 54. Such filler 54 may be of deformable material, forexample of hard gum. The bore 90 can then be drilled easily and with acommon drill. By making the diameter of filler 54 bigger, than the borein the piston 2, the bore 90 will be restricted to the needed narrownessby deformation of filler 54, when it is pressed or inserted into thebore in the piston 2. This makes any narrowness desired possible withoutthe need of expensive too small drills.

It has been found in accordance with this invention, that the drawbacksof the assembly of FIG. 1 resulted in cases of high pressures and speedsin a reduction of the efficiency of respective fluid handling devices bymany percent and as high as until 15 percent. The assembly of FIGS. 2and 3 reduced the efficiency of respective devices under such highpressure and speed until 6 percent. By the assembly of FIGS. 4 to 7 ofthe invention, the reduction of the efficiency of the respective deviceat same pressure-speed condition is reduced to less than 1.5 percent andin the assembly of FIGS. 8 and 9 of the invention it is reduced to lessthan 1 percent under same or equal pressure and relative move-speedconditions. The further increase in reduction of friction and/or leakageand thereby the further increase of the efficiency of the fluid handlingdevice with the assembly of FIGS. 8 to 9 of the invention is therebyobtained, that the bearing face area is still further increased, thesize of the balancing recess is still further increased and thestiffness of the tangent 51, if drawn, is reduced to an almostflattness. This is done thereby, that the radius 75 around the axis 76of the pivot bar 1 is increased to be about 0.8 to 1.3 of the size ofthe radius 55 of the piston, 2. The piston embracement portion 62 ofFIG. 5 is then no more existing. Equal referentials of FIGS. 8 and 9with those of FIGS. 4 to 7 are citing similar means. In FIGS. 8 and 9the said means are wider or more extended than in FIGS. 4 to 7. Becausethe radius 75 of FIGS. 4 to 7 is only 0.6 to 0.8 of the size of thepiston-radius 55. In order to prevent escape of the pivot portion 1 awayfrom the bed of piston 12 of FIGS. 8, 9 an assembly means, for examplepin 17 is assembled through pivote portion 1 and piston 12. Holdingmeans, like bar 18, head of pin 17 within pivote bar 1, spring means 20and holders 19 may be associated to the assembly pin means 17.Respective spaces in piston 12 and pivote bar 1 or piston shoe 11 may beprovided. As far as leakage might escape through bores, recesses orspaces, closure devices, for example 82 may be provided for example inspace 81 and contained therein or be fastened therein by retainers, forexample by retainer 83. Bar 18 may be parallel to the axis 76 orsurrounding it and may closely fit in a respective bore in pivot bar 1.A recess 84 may be provided in pivot bar 1 or in piston 12 for enablingthe pivoting motion of the pivot portion 1 by prevention of touch of pin17 to neighbouring parts and for provision of the ability to pivotrelatively between pin means 17, pivot bar 1 or piston 12.

Passages 10 are provided to pass fluid into balancing recesses 63 in thepiston shoe's outer face. This provision is not a novel means of theinvention. It is however novel and a means of this invention, to extendthem from the balancing recesses 63 into the deeper portions of thebalancing recess 3 beyond the control corners 8.

The pivot members 1 in pistons 2 with the improvements by this inventionare mainly provided and associated to pistons and piston shoes in radialpiston devices. It is however also possible to utilize them and to applythem in hydrostatic swing bearings or in hydrostatic pivot bearings.There they may serve different applications and not only fluid handlingradical piston devices. The axis of the pistons, for example axis 95 ofFIG. 4, will be called "a first axis"; the axis 76 for example of FIGS.2,6,8 will be called "a second axis" and the axis 96 of FIG. 9 will becalled "a third axis" and the point 30 of FIG. 6 will be called "an axiscentre point" in the appended claims.

What I claim is as follows:
 1. A hydrostatic pivot bearing consisting of a first body, a second body, bearing faces therebetween and a hydrostatic fluid pressure pocket in at least one of said bearing faces;wherein said first body is of substantially cylindrical configuration around a first axis, wherein said first body has a bearing bed face of part-cylindrical configuration around a second axis, wherein said second axis extends normally to said first axis and through said first axis, wherein said second body has a part-cylindrical pivot-portion with a bearing face of part-cylindrical configuration around said second axis, wherein said bearing bed face and said bearing face of part-cylindrical configurations have substantially equal radii around said second axis; wherein said first axis and said second axis are meeting in an axes centre point; wherein said bearing face of said second body is borne on said bearing bed face of said first body and able to slide therealong when said second body pivots on said first body while said faces are remaining at all times in close engagement along each other for sealing said fluid pressure pocket therebetween to prevent leakage thereout; wherein said second body has a third axis extending normal to and through said second axis and extending through said axes centre point whereby said third axis extends through said second and said first axis; wherein said third axis swings through said first axis when said second body pivots relatively to said first body; and wherein an improvement is provided which consists therein, that said part-cylindrical pivot-portion of said second body is provided with ends of part-cylindrical configuration of substantial radius around said third axis, whereby the length of the bearing area between said bearing faces is slightly shorter than the outer diameter of said first body for the provision of a maximum of bearing face area for the obtainment of the capability to carry a maximum of load by said bodies.
 2. The bearing of claim 1 wherein a fluid pressure communication recess is provided through said first body to said fluid pressure pocketand wherein said fluid pressure pocket extends through said bearing face of said second body into said part-cylindrical pivot-portion with said ends of part-cylindrical configuration of said second body.
 3. The bearing of claim 2, wherein said fluid pressure pocket is formed with end walls of part-cylindrical configuration around said third axis and wherein said endwalls of said fluid pressure pocket have smaller radii around said third axis than said radius of said ends has around said third axis whereby said bearing face of said second body is reduced to include bearing face portions of a length of the difference between said radius and one radius of said radii.
 4. The bearing of claim 3, wherein said end walls of said fluid pressure pocket are inclined inwardly in said second body for forming rigid end portions on said part cylindrical portion of said second body.
 5. The bearing of claim 4, wherein control corners are provided in the medial portion of said part-cylindrical pivot portion of said second body and wherein enlarged recesses extend between said control corners and said endportions beyond said control corners into said portion of said second body.
 6. The bearing of claim 2 wherein said part-cylindrical pivot portion is defined by a radius around said second axis of a size of 0.8 to 1.3 of the radius of the outer face of said first body around said first axis of said first body.
 7. The bearing of claim 1, wherein a retaining means is associated to said first and second bodies for retaining said bearing faces of said bodies closely together for sealing engagement of said bearing facesand wherein a space is provided for said retaining means to enable said retaining means to move in said space.
 8. The bearing of claim 7 wherein a bore is provided in said pivot-portion of said second body around said second axis and parallel to said second axis,wherein a bore is provided through said first body around said first axis and parallel to said first axis, wherein a bore is provided in said second body around said third axis and parallel to said third axis, wherein a holding pin is provided with a reception bore therethrough, wherein said holding pin extends into said bore around said second axis whereby said reception bore locates around said third axis and wherein a fitting pin means extends through said first body bore and is connected to said first body via spring means and extends through said reception bore and is connected to said holding pin by a pin means head, said bores and pins defining said retaining means; whereby said first and second bodies are fastened together and said second body is able to pivot on said bearing bed face of said first body.
 9. The bearing of claim 8 wherein closure means are provided in said bore around said third axis in order to close a portion of said bore around said third axis.
 10. The bearing of claim 1, wherein said first body is a piston, wherein said second body is a piston shoe and wherein said pivot-portion of part-cylindrical portion is longer in the direction of said second axis than one half of the entire length of said piston shoe in the direction of said second axis. 